In the UK we use .ac.uk, it was (when I was a student) my experience that places that say '.edu discount' generally also accepted my '.ac.uk' - I only recall one that didn't, and that was resolved after a support email.

I wonder if .edu is more strictly controlled in America though, because I still have an alumni.*.ac.uk address, which presumably anyone with automated handling of it would still accept. (Unless I suppose that's also common over there and they filter it out, and hope for no Mr Al Umnus from Scunthorpe.)

ac stands for academic so it has the same function as a 2LD as edu.